what happens if i use firecement mixed with sand for the insulating layer under the firebricks? The layer under the insulation is from normal cement with rebar in it.

james

05-21-2007 04:54 AM

Re: use firecement mixed with sand for the insulating layer ?

Welcome aboard Dr.

How thick were you thinking of going? I have seen plans (though never done it personally) that call for 6" of sand held in place with a single row of block or brick. If you don't have access to either insulating panels, vericulite or perlite, I think pure sand is your next best option. You don't have to mix it with anything.

Would other folks agree with that?
James

Dr.Pizza

05-21-2007 06:23 PM

Re: use firecement mixed with sand for the insulating layer ?

Thanks for welcome James. And by the way let me tell you that the fornobravo website is the best website i ever seen. So much informations. The story, the forum, the shop. Its great. What a luck i found it in the net. Studied a lot and started some days ago to build the 42" Toscana oven.For the insulation layer, i have allready done it. :o That is the problem, because i am afraid the oven dont work very well with this option. But i dont have access for vericulite or perlite. I mixed sand with firecement and little water that for an oatmeat consistance. Made a layer of 4". Down under 3.5" standard concrete. Both layer with rebar. Is that okay, or will i loose now a lot of heat? Or is it to much thermal mass? But hope you will tell me should be ok... otherwise i have to destroy it. But thats a lot of work. The layer is already hard. What you think?
Greetings from Thailand

Dr.Pizza

05-21-2007 09:55 PM

Re: use firecement mixed with sand for the insulating layer ?

James, a mistake. No sand....pure firecement under the cookingfloor. 4" thick.
Should it work?

james

05-22-2007 03:33 AM

Re: use firecement mixed with sand for the insulating layer ?

Got it. Can you describe firecement in a little more detail? What is it?

Even if you need a little more insulation, you don't have to take out what you have made. One option might be to put a layer of sand on top of what you have made, and raise your cooking floor a little bit. I think it depends on what firecement is made up of.

Let us know.
James

Dr.Pizza

05-24-2007 08:43 AM

Re: use firecement mixed with sand for the insulating layer ?

james, nobody can answer here about what firecement is made of. But anyway i have done it already and now i work at the dome (3. row). The oven looks good and i can just hope it will work with this materials. I will post pictures about that soon. Its a pompeii 47" (not 42). Have make pictures. My next question is about the chimney. Do i need a chimney because i want run the oven with gas. Not sure about that. Its a big and interesting projekt for me.

Greetings
dennis (dr.pizza)

jengineer

05-24-2007 10:01 AM

Re: use firecement mixed with sand for the insulating layer ?

Dr.Pizza

the reason James wants to know more about the firecement is due to its thermal properites. One kind of firecement will conduct (suck up) a lot lot heat and is used in making fire places while another kind can act as an insulator and is used in making kilns and boilers for steam generation. No-one has yet used this as there are better materials available for the insulating later.

Scenario one - Concrete hearth with firecement (Absorbs heat) on top of it and then a firebrick floor on top of that.
This oven will absorb a lot of heat from your fire. The heat will migrate down through the fire cement and into the concrete layer. This heat will equalize out and can be used for cooking long after the fire it removed. This floor will take longer to heat up than a typical Pompeii design.
Scenario two - Concrete hearth with firecement (insulating) on top of it and then a firebrick floor on top of that.
I suspect that it is slightly better than scenario one but will probably still absorb a fair amount of heat.

It may be a good thing that you are planning on using gas but you will probably still want to suplement it with wood as natural gas can add quite a bit of moisture due to the combustion products.

thanks a lot engineer! i think i have the insulating firecement because the guys here in thailand recomment it for insulating. Think i can not get anything better. Maybe in Bangkok, but that is too far away. Would you build the oven like me and look out if it works or would you destroy the insulation layer and build up something new?
i am not using natural gas. Will use LPG (Liguid Propan Gas). Equalent problem natural gas?

Dr.Pizza

05-25-2007 02:35 AM

Re: use firecement mixed with sand for the insulating layer ?

I also forget to ask what is refractory mortar. I can find a lot of definition on that. Here in thailand i can buy the normal Portland cement, fireclay, firemortar, firecement. Can i use firemortar mix it with sand 1:4 ? Or means firemortar=refractory mortar and i use it pure for fix the bricks. Totally confused. ..

james

05-25-2007 03:05 AM

Re: use firecement mixed with sand for the insulating layer ?

Dr. Pizza,

You definitely make your own mortar with 1 part Portland cement: 3 parts sand: 1 part fireclay (it's a powery clay): 1 part lime (a typical masons lime). You need the Portland cement as the binder that makes your mortar "set". Many of the Pompeii ovens were build with that recipe, and the components should be easy to find.

On the vent and gas-fired. First, yes you want a vent and chimney. There are descriptions of how to do that in the plans.

Be careful with gas. Your oven will be fully enclosed, so leaked gas won't have anywhere to escape -- which could be dangerous. I don't really like gas-fired residential ovens that are fired on weekends -- not constantly fired for a restaurant.